This application claims the priority of German patent Application No. 100 48 899.4 filed Oct. 2, 2000, which is incorporated herein by reference.
The invention relates to a cutting insert, such as the ones used in cutting tools for the machining of work pieces.
Milling cutters and other tools used for the machining of work pieces are frequently provided with one or several cutting inserts, which have a certain limited service life and therefore must be exchanged from time to time. Cutting inserts with only one cutting edge are replaced at that time. Cutting inserts with several cutting edges frequently can be turned inside the holder, meaning the insert can be turned to allow a cutting edge, which has not yet been used, to be placed in the active position. If necessary, the cutting insert can be used further by inserting it into a different holder to allow the use of a previously unused cutting edge.
Caution must be exercised with the above-described operation to prevent previously unused cutting edges from being turned or replaced, as well as to prevent that previously used cutting edges are not detected and are overlooked when replacing or turning the cutting inserts.
A cutting insert provided with a combination coating is disclosed in European Patent reference EP 0908259 A2. The chip surface is provided with a material that is not sensitive to impact and has a wear-reducing top surface with a low frictional value. The flank surface, on the other hand, is provided with a cutting material or a cutting material composition with higher abrasion resistance and hardness than the cutting material or the cutting material combination of the coating on the machining face. This is intended to improve the flank wear as well as the top surface quality and the dimensional accuracy of the work piece.
The above-explained problems are not solved with this method.
Thus, it is the object of the invention to create a cutting insert, which makes it easier to maintain the machining tools, in which this cutting insert is used.
The above object generally is achieved according to the present invention by a cutting insert comprising: a basic body including a bottom surface, side surfaces, and a top surface, of which at least one surface functions as a machining face and at least one other surface functions as a tool flank, a wear indicating layer provided on the tool flank, with the wear indicating layer having a color that differs from the color of the underlying flank surface.
The flank or flanks of the cutting insert according to the invention is (are) provided with a wearable indicating layer, having a color that differs from the color of the surface or layer underneath. The highest possible color contrast is aimed for in this case. The indicating layer deposited on the flank has a composition that clearly shows machining traces, if possible after only a short operating time of the cutting insert. For example, clear traces should appear after just a few minutes of a machining operation and the coating should be removed at least partially, so that the underlying base with different color becomes visible. The indicating layer of a possible embodiment is therefore not wear-resistant. On the contrary, that indicating layer is relatively sensitive to wear; e.g. it can have poor adherence to the base layer. However, it also possible to provide a well-running indicating layer that changes color as soon as the cutting insert is used.
The indicating layer can additionally or instead be sensitive in other ways in order to show that the respective neighboring cutting edge has already been used. For example, the indicating layer can be heat-sensitive and can show a change in color when heated above a limit temperature of 200xc2x0 C., for example, which occurs only in the vicinity of an active cutting edge. The color can change due to oxidation or other changes and is preferably irreversible. If the neighboring cutting edge was used only briefly and the corresponding flank area that adjoins the cutting edge has assumed at least briefly a temperature above the limit temperature, then the indicating layer changes to the color which remains visible over the long range. The advantage of a color change due to thermal effects is that even those flank areas that do not come into direct contact with the work piece during the operation change color.
Due to the aforementioned indicating layer, it is easy to see whether the cutting inserts of a cutting tool have already been used and which cutting edges are still unused, so that the cutting inserts can be replaced or turned. In particular, it is possible to avoid overlooking already used cutting inserts during the maintenance, or to replace unused cutting inserts, or to move previously used cutting edges again to the active position when turning the cutting inserts, or for unused cutting edges to remain unused. The maintenance of respective cutting tools is thus considerably simplified with the cutting insert according to the invention.
The indicating layer is preferably of a light color, e.g., yellow or with a silvery shine, whereas the machining face is preferably of a dark color. The machining face is preferably provided with an aluminum oxide coating (Al2O3), wherein additional layers can be provided underneath or on top of the Al2O3 layer. The cutting insert thus can be coated with several layers, wherein the Al2O3 layer forms the wear-reducing layer. However, it can also have additional top layers. Other wear-resistant layers with the same or better properties can also be provided in place of the Al2O3 layer.
In order to produce a cutting insert according to the invention, it is preferable if a wear-reducing coating, which may contain an Al2O3 layer, is initially applied to the complete basic body, meaning to the side or flank surfaces, the top surface and, if necessary, also the basic surface. For example, a nitrite-containing layer can be deposited as the top layer (e.g., TiN). This layer is preferably provided so as to cover the complete surface and is then removed from those surface areas, which are subjected to higher wear. The nitrite-containing layer, intended to serve as an indicating layer, in particular is preferably removed from the machining face through mechanical wear, e.g., a brushing operation or jet blasting (sand blasting). It is preferable if not only the machining face, but also the adjoining cutting edge is exposed, so that the indicating layer does not extend completely to the cutting edge.
The processing with a brush or jet at the same time represents a reworking of the cutting edge and the machining face, which simultaneously smoothes the coating in the area of the cutting edge and the machining face. This has a favorable effect on the machining sequence and helps increase the service life.
Advantageous details of the invention are the subject matter of the dependent claims and follow from the drawing or specifications.
An exemplary embodiment of the invention is illustrated in the drawing.